Electrolytic coatings are made on at least the surface of conductive parts, which are placed in baths with a precise composition and connected to the negative pole of a direct current source. The positive pole of the source is connected to conductive parts, called anodes, which are immersed in the bath.
In order that the deposition operation is correctly carried out and leads to a good quality coating, i.e. of constant thickness and with a good appearance, it is indispensable to prepare the surface of the part. This surface preparation involves the pickling of the part and the elimination of any foreign coating normally on the surface of the base metal, i.e. grease, oxide, calamine, etc.
In the case of the standard metals, such as iron, copper or alloys thereof, the existing processes give satisfactory results. However, these processes are not usable when the material to be coated is an easily oxidizable or corrodable metal, because coatings of oxides or products resulting from the pickling operation remain on the surface after the final washing. This is particularly the case with alloyed or unalloyed uranium.
In the case of metals of this type, it is necessary to use a process for the surface preparation of the parts, like that described in FR-A-No. 1 564 575. However, to obtain an electrolytic metallic deposit of constant thickness, other conditions have to be combined.
It is necessary for the parts to be coated to be transferred rapidly from one bath to another in order to prevent their oxidation on contact with air during the transfer time. It is also necessary for the orientation of the parts with respect to the current lines in the electrolytic bath do not lead to the deposition of an excess thickness at certain points on the part. For this purpose, it is necessary for the orientation of the part not to favour any portion of its periphery which can be obtained by rotating the part on itself, but this would involve a complex operation.
Finally, it is necessary to avoid excess thicknesses, which might occur on the part level with the electrolytic bath surface. Moreover, it is desirable for several parts to be treated simultaneously, in order to reduce the treatment time for each part.